Wall system



FIG. 1 is a perspective view of the ornamental design for a wall system in accordance with the invention;

FIG. 2 is a top view corresponding to FIG. 1;

FIG. 3 is a side view corresponding to FIG. 1;

FIG. 4 is a bottom view corresponding to FIG. 1; and,

FIG. 5 is a front view corresponding to FIG. 1. 

The ornamental design for a wall system, as shown. 